Lithium greases



United States Patent 3,153,574 LETHEUM GREASE John Greenwood, Didcot,and Ernes Augustus Saxon" Napier, Reading, Engiand, assignors to EssoResearch and Engineer-hag Company, a corporation of Deiaware No rowing.Filed Dec. 1, 19%, Ser. No. 156,4!3

Claims priority, appiieation Great Britain Dec. 6, 1968 5 Ciaims. {Ch22-36) This invention relates to a process for preparing greases derivedfrom a base lubricating oil and a lithium soap of a hydroxy fatty acid,and which contains an aliphatic polyhydroxy structure modifier, andparticularly relates to such a process in which the lubricity of such agrease is improved by incorporating the said polyhydroxy structuremodifier into a grease-forming composition at the maximum temperature ofthe constituents during manufacture.

A known method of manufacturing greases using lithium hydroxy soaps as agelling agent, is to incorporate the lithium soaps of hydroxy fattyacids (or constituents which produce such soaps) in a base lubricatingoil, which mixture is then heated to a temperature of about 180-220" F.whereby the mixture is dehydrated. The mixture is then further heated toa maximum temperature in the range of about 380420 F. The composition isheld at the maximum temperature for as short a time as possible toensure homogeneous heating, usually about minutes with stirring and thencooled to a setting temperature, i.e. at a temperature at which solidparticles first appear in the grease-forming composition. Duringcooling, and at a temperature usually, but not necessarily, below thesetting temperature, the grease-forming composition passes through aso-calied transition-temperature, which point is characterized by theevolution of heat from the cooling composition. The transitiontemperature can vary from one type of soap to another, and may in someinstances be above the maximum grease-forming temperature. After passingthrough the transition temperature, it is desirable to hold the greaseat an elevated temperature for an extended period of time to improve thefinal grease structure. This so-called heat-soak preferably occurs at atemperature below the transition temperature, and may range up to about75 F. below the transition temperature, and may extend for a period oftime of about 10 minutes to 4 hours.

It has previously been proposed that such a grease hav- I ing animproved structure may be obtained by incorporating a glyceride in theconstituents, from which the acid constituent of the grease-forming soapis derived. During manufacture the glyceri'de is hydrolyzed, resultingin a glycerol content of 1.3 to 1.5 weight percent based on the totalcomposition. While such a procedure may result in a grease of somewhatimproved structure, such greases derived from glycerides andmanufactured according to the procedure hereinbefore described are notalways successful in meeting present-day high duty lubricatingrequirements.

It has now been discovered that the lubricating properties of greases ofthe type hereinbefore described, i.e. derived from soaps of lithiumsoaps of hydroxy-substituted fatty acids, have their lubricatingproperties unexpectedly improved by the addition of a free aliphaticpolyhydroxy structure modifying agent at a particular stage of greasemanufacture, namely at or near the maximum temperature reached duringthe grease-manufacturing process as hereinbefore described. Thus thestructuremodifying agent is preferably added at a temperature within therange 375-425 F.

It is a preferred feature of this invention that oxidation inhibitingcompounds which are well-known constituents of grease compositions,should also be added at or near the aforesaid maximum temperature of thegrease-formlug constituents and particularly before the structuremodifying agent. It the anti-oxidant is added at a lower temperature,e.g. during thecooling ofthe grease or after the structure modifyingagent, the final grease is unexpectedly deficient in lubricatingproperties.

Particularly useful greases according to this invention are obtained byincorporating a small proportion of lead or zinc naphthenate therein inaddition to the polyhydroxy structure modifying agent. Proportions ofthe said naphthenate preferably range from 0.1 to 6%, preferably 1% to2.5% by weight, based on the total composition. Besides improvingthecorrosion-resistance of the greases in which they are incorporated, itappears that greases may be obtained which have equivalent lubricatingproperties but which contain somewhat smaller proportions of thepoly-hydroxy structure-modifying agent, than are necessary in theabsence of the'said naphthenates.

Greases prepared according to this invention, while showing improvedlubricating properties, also display lower transition points duringcooling of the grease-forming mixtures.

Aliphatic structure modifiers used in the process of this inventioninclude glycols, polyglycols, e.g. polyethylene or propylene glycols,the polyglycols preferably having a molecular weight between about 450and 650, glycerol, pentaerythritol, hexane 2,5 diol, and partial estersof sorbitol, e.g. sorbitan mono-oleate or stearate. The proportions ofpolyhydroxy compound used is preferably between 1% and 4% by weight,based on the total composition. In the case of glycerol, particularlyuseful results are obtained when the glycerol is present in proportionof about 2%. It is an essential feature of the invention that the freepolyhydroxy compound is incorporated in the grease-forming compositionat or near the maximum temperature.

Anti-oxidant compounds incorporated in the grease compositions of thisinvention are a usual and well-known class of compounds for greasecompositions, particularly nitrogen and/or phosphorus-containingcompounds and phenolic compounds, and include phenothiazine,alkylsubstituted phenothiazine phenyl-naphthylamine, alkylsubstitutedphenols, including 2,6'- and 2,4,6-substituted phenols for instance 2,6tert. butyl 4 methyl phenol substituted diphenylamines, for instancedi-octyl phenyla mine, and alkyl-substituted bisphenols, metal salts ofdialkyl dithio dithiophosphate including cadmium and zinc salts thereofand metal dithiocarbamates. These compounds incorporated in thegrease-forming composition according to this invention enables theimproved lubricating properties donated by the structure-modifyingcompounds to be preserved, often with a smaller proportion ofpolyhydroxy compound than would otherwise be necessary. It is preferredthat the anti-oxidant compound is added before the polyhydroxy structuremodifier is added.

The lithium soaps used as gelling-agents in the composition of thisinvention include soaps of-hydroxy-substituted C C fatty acid, forinstance lithium l2-OH stearate. The soap is preferably formed duringheating by interaction between lithlum hydroxide and the free acid.

A typical manner of manufacture according to this in vention is toincorporate a Gi -C hydroxy-substituted fatty acid in a major proportionof the lubricating oil, e.g. a mineral oil of viscosity 35-200 SUSS/210F., although synthetic oils may be used, and heat to a temperature ofabout 180 F., thereafter slowly adding lithium hydroxide dissolved inwater in a total amount to form a soap with the fatty acid. The amountof fatty acid added in the first instance should be sufiicient to formthe desired greaseconsistency in the final composition when it iscompletely saponified. The actual amount of fatty acid used willtherefore depend on the particular acid used, the nature of the baseoil, and the use for which the grease is intended. As a general guidehowever, from 4% to 25% by weight based on the lubricating oil, may beincorpo rated. After the lithium hydroxide is added, the mixture isheated to 300 F. with stirring for a period of time until the waterpresent has been removed. The mixture is then further heated to atemperature of about 375-425 '1, and the anti-oxidant compound,preferably dissolved in the remainder of the base oil (eg. in about 2%to 6% of the oil) is added, followed by the addition with stirring ofthe aliphatic polyhydroxy structure-modifying agent in proportionspreferably of the order of 1% to 4% by weight. The mixture is thencooled as quickly as possible to about 375 F., and then further cooledat a slower rate, to reach about 315 F. The grease mixture is then heldat this temperature for a period of time about 15 minutes to 2 hours,and then cooled to 140 F. The mixture is continuously stirred whilecooling. The grease is homogenized, for instance in a colloid mill, anddeaerated.

Particular embodiments of this invention are hereinafter described.

Four greases were prepared, comprising a mineral base oil thickened to agrease consistency with lithium hydroxy stearate, and containing phenylfl-naphthylamine as an anti-oxidant. Grease A contained nostructure-modifying agent. In Grease B the lithium soap was derived froma glyceride of 12-OH stearic acid hydrolyzed at a low temperature toproduce the fatty acid. Grease C was prepared according to thisinvention, containing 2% by weight of glycerol as a structure-modifyingagent added to the grease-forming composition at the maximum 0temperature, e.g. 400 C. Grease D was similar to Grease C, except thatthe anti-oxidant was added at a lower temperature after the glycerol.

Grease A Grease A was prepared from a composition consisting of:

Weight Percent Lithium hydroxide monohydrate 2.1 12-OH stearic acid 13.3Phenyl {i-naphthylamine 0.9 Mineral oil viscosity 110 cs./ 100 F 83.7

315 F., and held at this temperature for 2 hours. The A gelled mixturewas then further cooled to 140 F., and milled in a colloid mill with0.006" to 0.015 mill clearance, and then deaerated. The composition wascontinuously stirred during manufacture.

Grease B Grease B was prepared in a similar manner to Grease A, exceptthat the fatty acid was derived from 12.8 wt. percent of the glycerideof 12-OH stearic acid. The gly- -ceride was dissolved in its own Weightof oil, saponified with the lithium monohydrate, 25% of the total baseoil added, dehydrated at 300 F., the remainder of the base oil added,(less 4%), heated to 400 F., cooled to 315 F., the anti-oxidant added in4% of the oil solution and the grease finished as Grease A. The finalgrease contained 1.3% of glycerol.

Grease C Grease C was prepared in a similar way to Grease A, except thatthe anti-oxidant was added at the maximum temperature of 400 F., afterwhich 2% of glycerol as a structure-modifying agent was also added whilethe mixture was still at the same high temperature.

Grease D Grease D was also prepared in a similar way to Grease C, exceptthat the anti-oxidant was added to the composition after the glycerol,at a temperature of 320 F., i.e. while the grease-forming mixture wascooling.

The above four greases were tested in the Hoffman High Speed Rig.

TABLE I Hofiman High Speed Penetration Transition Big Test; Grease(X60)mm./l0, Point, F.

ASTM D217 Hours Cage Wear,

Run inches 238 400 500 0.021 242 366 168 0. 016 223 344 500 NIL 289 330500 0. 000

1 Prepared according to the invention.

It will be observed from Table I that the lubricating properties ofgreases as exemplified by the cage wear are greatly improved when apolyhydroxy structure modifier is included in the formulations when thelatter are at the maximum temperature, and also that the best resultsboth from yield and anti-wear properties are obtained when theanti-oxidant and the polyhydroxy compound are both added when thegrease-forming composition is at the maximum temperature, as shown byGrease C.

Greases of enhanced corrosion resistance may be obtained according tothis invention by incorporating small proportions up to 5%, preferably0.5 to 2.5% by weight, of zinc or lead naphthenate. In such instancesgreases of comparable structure and properties may be obtained withproportions of polyhydroxy structure-modifiers substantially reducedover the proportions used in the absence of the naphthenates. Anti-wearadditive compounds may also be incorporated in the composition of thisinvention, particularly molybdenum disulphide.

What is claimed is:

1. A process for preparing a lubricating grease composition whichcomprises:

(a) incorporating a grease-forming amount of lithium soap of: 0 -0hydroxy fatty acid in a lubricating oil vehicle to thereby form amixture,

(b) heating said mixture for a period of time sufiicient to causedehydration,

(c) further heating said mixture to a maximum term perature of about375425 R,

(d) adding from 1-4 weight percent of glycerol, based on the totalweight of said grease composition, to said mixture at about said maximumtemperature, and

(e) cooling said mixture to form said grease composition.

2. A process as defined in claim 1 wherein an anti-oxi dant forlubricating greases is also added to said mixture at about said maximumtemperature.

3. A process as defined in claim 2 wherein said antioxidant is addedprior to said glycerol.

4. A process as defined in claim 3 wherein said antioxidant is phenylbeta naphthylamine.

5. A process as defined in claim 4 wherein from 0.1 to 6.0 weightpercent of a material selected from the group consisting of leadnaphthenate and Zinc naphthenate is also-added to said mixture.

References Cited in the file of this patent UNITED STATES PATENTS Re.23,243 Bondi June 20, 1950' 2,449,312 Murray et al Sept. 14, 19482,450,221 Ashburn et al Sept. 28, 1948v 2,470,965 Woods et al May 24,1949 2,487,081 Swenson Nov. 8, 1949 2,666,033 Dilworth et a1 June 12,1954 2,812,306 Liehe Nov. 5, 1957 2,895,914 Kern et al. July 21, 1959

1. A PROCESS FOR PREPARING A LUBRICATING GREASE COMPOSITION WHICHCOMPRISES: (A) INCORPORATING A GREASE-FORMING AMOUNT OF LITHIUM SOAP OFC12-C24 HYDROXY FATTY ACID IN A LUBRICATING OIL VEHICLE TO THEREBY FORMA MIXTURE, (B) HEATING SAID MIXTURE FOR A PERIOD OF TIME SUFFICIENT TOCAUSE DEHYDRATION, (C) FURTHER HEATING SAID MIXTURE TO A MAXIMUMTEMPERATURE OF ABOUT 375-425*F., (D) ADDING FROM 1-4 WEIGHT PERCENT OFGLYCEROL, BASED ON THE TOTAL WEIGHT OF SAID GREASE COMPOSITION, TO SAIDMIXTURE AT ABOUT SAID MAXIMUM TEMPERATURE, AND (E) COOLING SAID MIXTURETO FORM SAID GREASE COMPOSITION.